Peroxidic bleach containing silicic acid ester



United States Patent 3,003,910 PEROXIDIC BLEACH CONTAINING SILICIC ACID ESTER Karl Dithmar, Frankfurt am Main, Germany, assignor tii The present invention relates to a method of stabilizing the active oxygen content of textile bleaching baths.

The object of this invention to to provide a chemical stabilizer which will regulate the decomposition of peroxide compounds in textile bleaching baths.

Another object of this invention is to provide such a stabilizer which is unaffected by the presence of heavy metals or heavy metal compounds in the bleaching bath.

Another object of this invention is to provide a stabilizer, the presence of which will not have a detrimental efiect on the materials .to be bleached.

'It has been known for some time, of course, that fibrous and textile materials can be treatd with aqueous solutions or dispersions of peroxidic compounds which yield active oxygen. Compounds which fall into this class are, for example, hydrogen peroxide, sodium peroxide, and the salts of perboric acid, percarbonic acid, perphosphoric acid and the like. For the stabilization of these solutions or dispersions, an alkali metal silicate in combination with soluble magnesium and calcium salts is frequently resorted to. The addition of these stabilizers acts to prevent a too rapid decomposition of the per-compounds. The magnesium or calcium silicates that result from these chemical combinations have proven to be well suited for the task of stabilizers. Their use, however, in this regard is not without serious drawbacks since they produce a turbidity in the bath, particularly as the bath cools off and sediment containing silicic acid is deposited on the fibers.

The use of organic stabilizers, which contain calcium or magnesium combined in organic salt formers oncomplexes, is also known to be old in the art. With these compounds the bleaching baths can also be adequately stabilized. However, the use of these organic stabilizers also entails disadvantages, in that their eiiectiveness is curtailed by the presence of small amounts of heavy metals or heavy metal compounds contained in the fibers. When these metals or compounds are present the decomposition of the peroxides is catalytically accelerated, and because of this a localized overbleaching of the fibers can readily occur which effects their value and use. It is also possible for the situation to occur wherein the organic stabilizers, which also act as dispersing agents, will distribute over a wide area of the fabric, the heavy metal impurities, which might otherwise be found mainly concentrated, point'like, in single places. In that case then, instead of pinpoint reactions on the fibers, a larger portion of the fibers would be injured by the catalytically increased oxidation.

A good deal of work has been done in the past in trying to dissolve out the heavy metal impurities with the aid of different solvents. However, up to the present time, it has not been possible to effect a complete removal of the heavy metals. The use of metal complex formers moreover cannot be economically justified in many cases.

The old type silicate stabilizers have been used mainly with concentrated and alkaline peroxide baths. As was noted above, however, these stabilizers have their drawbacks, in that they cause turbidity in the bath as the bath cools off and consequently the silicate may deposit on the fibers.

According to this invention, it has now been found,

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acid, so that there is always suflicient stabilizer available to retard the rapid decomposition of the peroxidic compounds. In addition, the slow decomposition of the silicic acid ester avoids turbidity in the bath as well as a deposition of silicates on the fibers or textiles.

Furthermore, it has also been found, according to the invention, that alkoxysilanes can be used with excellent results as the silicic acid esters. These alkoxysilanes are soluble in water and exhibit excellent stabilizing charack teristics. Typical al'koxysilane's, for example, are tetrakis- (2 methoxy ethoxy) silane, methyl-tris 2 methoxyethoxy) silane and dimethyl-bis (2-methoxy-ethoxy)- silane.

The stabilizing effect of the silicic acid esters can be increased if, in addition, water soluble alkali metal salts or particularly water soluble alkaline earth metal salts, such as salts of magnesium or of calcium, are added to the bleaching baths.

Furthermore, the treatment of the textiles and fibers in the presence of silicic acid esters is preferably conducted in an alkaline medium, for example, at a pH between 7.5 and 11.5. For the attainment of the desired pH the usual buffering salts, such as phosphates and the like, can be employed.

Particularly good results can be obtained if the bleaching operation is COlldllCtedJfit temperatures over 60 C., preferably between C. and C. In addition, the usual chemical textile aids can be used in the bleaching bath according to the process of this invention, such as the sodium salt of dodecyl sulfate, oxyethylated fatty alcohols with 12 to 16 C-atorns or the condensation products of proteins with aliphatic acids.

For an evaluation of the stabilization eifect of a silicic acid ester, a comparison has been made between the stabilizing effects of a silicic acid ester and sodium silicate. The following table depicts the active oxygen content of several bleaching solutions which have been maintained at 60 C. Periodic tests were made on these solutions at hourly intervals over a period of six hours to determine their respective active oxygen contents at these times. All the solutions originally were charged with enough hydrogen peroxide to impart an active oxygen content of 1.8 g./ liter thereto. In addition, all the solutions contained 0.1 g./ liter of magnesium sulfate containing water of crystallization. Solution I contained no other additives but solution II contained sodium silicate and solution III contained tetrakis-(Z-methoxy-ethoxy)- silane, each in such quantities that the SiO content of solutions 11 and HI each amounted to 0.334 g./liter. In all solutions the pH was adjusted to 9.0.

TABLE Hours Thus, it is clear that the addition of the silicic acid ester stabilized the hydrogen peroxide equally as well as the addition of the sodium silicate when both compounds were used in combination with magnesium sulfate. The apparent rise in the active oxygen content is explainable o by the fact that when the solutions were heated to 60 C.

1 kg. of: fabric having a cotton warp and woof, which had previously been boiled in an alkaline medium, was treated for 2 'hoursat 95 C. in a peroxidic bleaching bath. The bath to fabric ratio was 12:1 and the chemical composition of the bath per liter of soft water was as follows:

G. Hydrogen peroxide (35% by weight) 0.1

Tetrakis-(2-methoxy-ethoxy)-silane 1.8 Sodium hydroxide 0.3 Oxyethylated dodecyl alcohol 0.3

After this treatment the cotton fabric was rinsed and dried in the usual manner. The traces of cotton seed shells, which always make the fabiic unattractive, had been so sufficiently dissolved and loosened by the treatment in the bath that they fell out when the fabric was stretched. When tested, the whiteness content of the treated cotton fabric was found to be 84% of the MgO reference plate of a Zeiss-Elrepho whiteness meter. The untreated cotton fabric had a whiteness content of 54% when similarly tested.

The active oxygen content of the bleaching bath in the example which initially amounted to 1.8 g./ liter, was lowered to 0.89 g./liter due to the bleaching operation conducted on the cotton fabric.- Simultaneously, the pH dropped from an initial value of 9.8 to 9.2.

A fabric having a polyester fiber warp and woof when bleached under the same conditions exhibited an equally good increase in whiteness efiect.

Example 2 45 kg. of a fabric made of Nylon 6, which was-previously thermofixed at 182 C. and desized, was treated in a jigger for 2 hours at 100 C. with 300 liters of a bleaching bath containing After this treatment the fabric was twice rinsed with warm water and once with cold water and dried in the usual manner. The whiteness of the treated fabric was found to be 81% of the MgO reference plate of a Zeiss- Elrepho whiteness meter. The active oxygen content of the bleaching bath in the example which initially amounted to 1.5 g./liter was lowered to 0.33 g./liter due to the bleaching operation.

The silicic acid esters according to the invention are hydrolysable when added to an alkaline reacting solution.

I claim:

1. In a process for bleaching cellulose, wood pulp, natural and synthetic fibers in an aqueous medium containing a peroxidic bleaching compound, the step which comprises incorporating an at least partially water soluble, hydrolyzable, silicic acid ester in the aqueous medium employed for such bleaching to maintain a quantity of silicic acid ester of 1 to 30 g. per liter in said aqueous medium.

2. A process as in claim 1 in which the said silicic acid ester is an alkoxy silane.

3. A process as in claim 1 in which the active oxygen content is maintained in the range of 0.1 to 15 g. per liter.

4. A process as in claim 1 in which the bleaching is conducted in the presence of a water soluble salt selected from the group consisting of water soluble alkali metal salts and water soluble alkaline earth metal salts.

5. A process as in claim 4 in which the amount of said water soluble salt used is in the range of 0.005% to 0.1% relative to the amount of the said aqueous medium;

6. A process as in claim 1 in which said peroxidic bleaching compound is hydrogen peroxide.

7. A process as in claim 1 in which the said aqueous medium is maintained in an alkaline range.

8. A process as in claim 1 in which the bleaching is conducted at temperatures over C.

9. An aqueous bleaching bath containing a peroxidic bleaching compound and an efiective amount of an at least partially water soluble, hydrolyzable, silicic acid ester to act as a stabilizer for said peroxidic bleaching com pound.

10. A bleaching bath as in claim 9 in which the said silicic acid ester is an alkoxy silane.

11. A bleaching bath as in claim 9 in which the said .peroxidic bleaching compound is hydrogen peroxide.

12. A bleaching bath as in claim 9 further comprising water soluble salts selected from the group consisting of alkali metal salts and alkaline earth metal salts.

13. A process as in claim 1 in which the amount of the silicic acid ester is in the range of 50 to relative to the amount of active oxygen.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A PROCESS FOR BLEACHING CELLULOSE, WOOD PULP, NATURAL AND SYNTHETIC FIBERS IN AN AQUEOUS MEDIUM CONTAINING A PEROXIDIC BLEACHING COMPOUND, THE STEP WHICH COMPRISES INCORPORATING AN AT LEAST PARTIALLY WATER SOLUBLE, HYDROLYZABLE, SILICIC ACID ESTER IN THE AQUEOUS MEDIUM EMPLOYED FOR SUCH BLEACHING TO MAINTAIN A QUANTITY OF SILICIC ACID ESTER OF 1 TO 30 G. PER LITER IN SAID AQUEOUS MEDIUM. 